[Skiboot] [PATCH 3/3] ipmi/wdt: Add ipmi watchdog timer support

[Benjamin Herrenschmidt]

On Thu, 2015-01-29 at 15:00 +1100, Alistair Popple wrote:
> On Thu, 29 Jan 2015 11:56:33 Benjamin Herrenschmidt wrote:
> > On Thu, 2015-01-29 at 08:54 +0800, Jeremy Kerr wrote:
> > > Hi Ben,
> > > 
> > > > Bah, petitboot kernel will start it and that's it, once it's started,
> > > > it's started and if we kexec something tat doesn't support it we are
> > > > toast anyway
> > > 
> > > My plan is to have petitboot disable the watchdog timer just before
> > > kexec. This way, we don't export this "ABI" beyond the petitboot
> > > environment, which we'd have control of anyway.
> > > 
> > > The OS kernel can re-enable it if necessary, but isn't required to.
> > 
> > Which means that if it fails to boot, we have no watchdog... I don't
> > like this *that* much...
> > 
> > Can the watchdog be tied to an interrupt from the BMC ? Something we
> > know we will react to unless the kernel is dead ?
> 
> Yes, there is a pre-timeout interrupt which works. So how about instead of 
> requiring the payload OS to disable it we just set a pre-timeout interrupt 
> prior to entering the OS? Once we see that interrupt in skiboot we can just 
> disable the WDT and then it's up to the payload to do what it wants with the 
> WDT through IPMI commands. If we never see the interrupt the WDT will trip and 
> the system will reboot.

Or we just set the pre-timeout interrupt always and use it as the
watchdog tickle.

Ben.